1. Field of the Invention
The present invention relates to improvements in a heat pump type air conditioner applied to an automotive vehicle, and more particularly to an air conditioner which is provided with a vapor-compression refrigeration cycle.
2. Description of the Prior Art
It is well known that a heat pump type air conditioner is applied to an automotive vehicle and provided with a four-way valve by which refrigerant flow is changed between a heating operation and a cooling operation. During the heating operation, an outer heat exchanger is used as a heat absorber, and an inner heat exchanger is used as a heat radiator. On the other hand, during the cooling operation, the outer heat exchanger is used as a heat radiator, and the inner heat exchanger is used as a heat absorber. Such a heat pump type air conditioner is disclosed, for example, in Japanese Patent Provisional Publication No. 2-290475 and Japanese Utility Model Provisional Publication No. 2-130808.
As shown in FIG. 31, during a heating operation, a four-way valve 2 is set as indicated by a continuous line in FIG. 31, and refrigerant is circulated as follows: A compressor 1 .fwdarw. the four-way valve 2 .fwdarw. a first inner heat exchanger 3 .fwdarw. a heating heat exchanger 4 .fwdarw. a second inner heat exchanger 5 .fwdarw. an expansion valve 6 .fwdarw. an outer heat exchanger 7 .fwdarw. the four-way valve 2 .fwdarw. a receiver 8 .fwdarw. the compressor 1. Accordingly, the heat of the refrigerant is transmitted to air led by a blower fan 9 and used for heating a passenger compartment. The heat from an engine 10 is transmitted to the refrigerant through the heating heat exchanger 4 and further transmitted from the refrigerant to air led by a blower fan 11 for heating the passenger compartment. The heat of the air led by a fan 12 is transmitted to the refrigerant through the outer heat exchanger 7.
On the other hand, during the cooling operation, the four-way valve 2 is set as indicated by a broken line in FIG. 30 and refrigerant is circulated as follows: The compressor 1 .fwdarw. the outer heat exchanger 7 .fwdarw. the expansion valve 6 .fwdarw. the second inner heat exchanger 5 .fwdarw. the first inner heat exchanger 3 .fwdarw. the four-way valve 2 .fwdarw. the receiver 8 .fwdarw. the compressor 1. Accordingly, the heat of the refrigerant discharged from the compressor 1 is radiated into the atmosphere by the outer heat exchanger 7, the heat of air led by blower fans 9 and 11 is radiated to the refrigerant by the first and second inner heat exchanger 3 and 5, and the cooled air is supplied into the passenger compartment.
With such a conventional heat pump type air conditioner, the absorbed heat amount by the outer heat exchanger 7 is decreased during the heating operation under conditions such that the ambient temperature is low, the automotive vehicle is in running, or it is raining or snowing. Furthermore, if the workload of the compressor 1 is constant, the radiated heat amount from the first and second inner heat exchangers 3 and 5 which radiate the sum of the heat absorbing amount from the outer heat exchanger 7 is decreased, and the heating capacity of the air conditioner is lowered. Additionally, the lowering of the heating capacity invites the frost to the heat exchanger. This increases a defrost operation and prevents a stable heating operation. Furthermore, since the conventional air conditioner is arranged such that the flow direction of the refrigerant is changed under the cooling and heating operations, it is necessary to change the design of the conduits of the outer and inner heat exchangers 7, 3, and 5 so as to endure high temperature and high pressure.
Also, since the conventional heat pump type air conditioner is arranged to generate heated air for heating by utilizing the waste heat of the engine 10 during the heating operation, it can not be sufficiently operated if applied to a vehicle which only has small heat source, such as to a solar car or electric vehicle.
Furthermore, with the conventional heat pump type air conditioner, when it is started under a low ambient air temperature condition, an evaporation temperature of the refrigerant at the outer heat exchanger 7 is lowered due to a low air temperature to the outer heat exchanger 7. This lowers temperature and pressure of the refrigerant fed to the compressor 1.
Refrigeration capacity R and input W of the compressor 1 are represented by the following equations: EQU R=.eta.v.times..rho.v.times.V.times.q0 (Watt) EQU W=.eta.v.times..rho.v.times.V.times.AL(.eta.c.times..eta.m)(Watt)
wherein .eta.v is volumetric efficiency, tic is adiabatic compression efficiency, rim is mechanical efficiency, .rho.v is refrigerant density (kg/m.sup.3), V is compressor discharge (m.sup.3 /s), q0 is refrigerating effect (J/kg), and AL is adiabatic compression work.
Accordingly, if the temperature and/or pressure of the refrigerant fed to the compressor 1 is lowered, the volumetric efficiency fly and the adiabatic compression efficiency tic are degraded according to the increase of the compression ratio of the compressor 1, and the refrigerant density .rho.v is decreased. Since the change of the refrigerant density .rho.v becomes larger than that of the volumetric efficiency .eta.v, the adiabatic compression efficiency .eta.c, or the adiabatic compression work (J/kg); the refrigeration efficiency R and the input W of the compressor 1 is largely lowered by the main effect of the change of the refrigerant density .rho.v, as is clear from the above-equations. Accordingly, the heat radiation amount at the inner heat exchangers 3 and 5 becomes small, and therefore, it is difficult to operate the conventional air conditioner under low ambient temperature condition. Although it is possible to increase the input W of the compressor 1 by increasing rotation speed for the increase of the compressor discharge V, such increase of the rotation speed occurs problems such that the compressor 1 largely generates noise and vibration and degrades its durability.